545 research outputs found
From multifragmentation to supernovae and neutron stars
The thermodynamics properties of globally neutral dense stellar matter are
analyzed both in terms of mean field instabilities and structures beyond the
mean field. The mean field response to finite wavelenght fluctuations is
calculated with the realistic Sly230a effective interaction. A Monte Carlo
simulation of a schematic lattice Hamiltonian shows the importance of
calculations beyond the mean field to calculate the phase diagram of stellar
matter. The analogies and differences respect to the thermodynamics of nuclear
matter and finite nuclei are stressed.Comment: To be published in Acta Phys. Hung.
Nuclear symmetry energy and core-crust transition in neutron stars: a critical study
The slope of the nuclear symmetry energy at saturation density is pointed
out as a crucial quantity to determine the mass and width of neutron-star
crusts. This letter clarifies the relation between and the core-crust
transition. We confirm that the transition density is soundly correlated with
despite differences between models, and we propose a clear understanding of
this correlation based on a generalised liquid drop model. Using a large number
of nuclear models, we evaluate the dispersion affecting the correlation between
the transition pressure and . From a detailed analysis it is shown
that this correlation is weak due to a cancellation between different terms.
The correlation between the isovector coefficients and plays
a crucial role in this discussion
Giant Pulsar Glitches and the Inertia of Neutron-Star Crusts
Giant pulsar frequency glitches as detected in the emblematic Vela pulsar
have long been thought to be the manifestation of a neutron superfluid
permeating the inner crust of a neutron star. However, this superfluid has been
recently found to be entrained by the crust, and as a consequence it does not
carry enough angular momentum to explain giant glitches. The extent to which
pulsar-timing observations can be reconciled with the standard vortex-mediated
glitch theory is studied considering the current uncertainties on dense-matter
properties. To this end, the crustal moment of inertia of glitching pulsars is
calculated employing a series of different unified dense-matter equations of
state.Comment: 11 pages, 6 figures, submitted to PR
Cluster formation in compact stars: relativistic versus Skyrme models
We present various properties of nuclear and compact-star matter, comparing the predictions from two kinds of phenomenological approaches: relativistic models (both with constant and density-dependent couplings) and non-relativistic Skyrme-type interactions. We mainly focus on the liquid-gas instabilities that occur at sub-saturation densities, leading to the decomposition of the homogeneous matter into a clusterized phase. Such study is related to the description of neutron-star crust (at zero temperature) and of supernova dynamics (at finite temperature)
Isospin fractionation : equilibrium versus spinodal decomposition
This paper focuses on the isospin properties of the asymmetric nuclear-matter
liquid-gas phase transition analyzed in a mean-field approach, using Skyrme
effective interactions. We compare two different mechanisms of phase separation
for low-density matter: equilibrium and spinodal decomposition. The isospin
properties of the phases are deduced from the free-energy curvature, which
contains information both on the average isospin content and on the system
fluctuations. Some implications on experimentally accessible isospin
observables are presented
Isospin-dependent clusterization of Neutron-Star Matter
Because of the presence of a liquid-gas phase transition in nuclear matter,
compact-star matter can present a region of instability against the formation
of clusters. We investigate this phase separation in a matter composed of
neutrons, protons and electrons, within a Skyrme-Lyon mean-field approach.
Matter instability and phase properties are characterized through the study of
the free-energy curvature. The effect of beta-equilibrium is also analyzed in
detail, and we show that the opacity to neutrinos has an influence on the
presence of clusterized matter in finite-temperature proto-neutron stars.Comment: To appear in Nuclear Physics
Cluster formation in asymmetric nuclear matter: semi-classical and quantal approaches
The nuclear-matter liquid-gas phase transition induces instabilities against
finite-size density fluctuations. This has implications for both
heavy-ion-collision and compact-star physics. In this paper, we study the
clusterization properties of nuclear matter in a scenario of spinodal
decomposition, comparing three different approaches: the quantal RPA, its
semi-classical limit (Vlasov method), and a hydrodynamical framework. The
predictions related to clusterization are qualitatively in good agreement
varying the approach and the nuclear interaction. Nevertheless, it is shown
that i) the quantum effects reduce the instability zone, and disfavor
short-wavelength fluctuations; ii) large differences appear bewteen the two
semi-classical approaches, which correspond respectively to a collisionless
(Vlasov) and local equilibrium description (hydrodynamics); iii) the
isospin-distillation effect is stronger in the local equilibrium framework; iv)
important variations between the predicted time-scales of cluster formation
appear near the borders of the instability region.Comment: 27 pages, 11 figures, Submitted to Nuclear Physics A, Nuclear Physics
A In press (2008
Thermodynamics of compact-star matter within an ising approach
International Conference on Nucleus Nucleus Collisions 2006International audienceIn the formation and evolution of compact stars, nuclear matter explores high thermal excursions and is the site of intense neutrino emission. Neutrino transport as well as structural properties of this matter depend on the presence of inhomogeneous phases (named “pasta” phases), which are the result of Coulomb frustration of the Liquid-Gas phase transition. We take into account charge fluctuations by employing a frustrated lattice-gas model to which we impose a neutrality constraint by the addition of an homogeneous background of charge, representing delocalised electrons. Within this schematic model we highlight a generaic feature of the phase-transition phenomenology: the temperature interval where pasta phases are formed is enhanced by Coulomb-frustration effects. This result is at variance with the behaviour of frustrated ferromagnetic systems as well as hot nuclei and mean-field approaches. Moreover, the region of phase coexistence is not found to end upon a critical point, indicating that no critical opalescence can occur in compact-star matter
Phase diagram of neutron-rich nuclear matter and its impact on astrophysics
Dense matter as it can be found in core-collapse supernovae and neutron stars
is expected to exhibit different phase transitions which impact the matter
composition and equation of state, with important consequences on the dynamics
of core-collapse supernova explosion and on the structure of neutron stars. In
this paper we will address the specific phenomenology of two of such
transitions, namely the crust-core solid-liquid transition at sub-saturation
density, and the possible strange transition at super-saturation density in the
presence of hyperonic degrees of freedom. Concerning the neutron star
crust-core phase transition at zero and finite temperature, it will be shown
that, as a consequence of the presence of long-range Coulomb interactions, the
equivalence of statistical ensembles is violated and a clusterized phase is
expected which is not accessible in the grand-canonical ensemble. A specific
quasi-particle model will be introduced to illustrate this anomalous
thermodynamics and some quantitative results relevant for the supernova
dynamics will be shown. The opening of hyperonic degrees of freedom at higher
densities corresponding to the neutron stars core modifies the equation of
state. The general characteristics and order of phase transitions in this
regime will be analyzed in the framework of a self-consistent mean-field
approach.Comment: Invited Talk given at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
Role of isospin in the nuclear liquid-gas phase transition
We study the thermodynamics of asymmetric nuclear matter using a mean field
approximation with a Skyrme effective interaction, in order to establish its
phase diagram and more particularly the influence of isospin on the order of
the transition. A new statistical method is introduced to study the
thermodynamics of a multifluid system, keeping only one density fixed the
others being replaced by their intensive conjugated variables. In this ensemble
phase coexistence reduces to a simple one dimensional Maxwell construction. For
a fixed temperature under a critical value, a coexistence line is obtained in
the plane of neutron and proton chemical potentials. Along this line the grand
potential presents a discontinuous slope showing that the transition is first
order except at the two ending points where it becomes second order. This
result is not in contradiction with the already reported occurrence of a
continuous transformation when a constant proton fraction is imposed. Indeed,
the proton fraction being an order parameter in asymmetric matter, the
constraint can only be fulfilled by gradual phase mixing along the first-order
phase transition line leading to a continuous pressure.Comment: To appear in Nuclear Physics
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